This invention relates generally to hydraulic pressure devices and more particularly to a hydraulic pressure device adapted for use as an auxiliary release apparatus for a hydraulic pressure releasable brake having a principal source of hydraulic pressure when the principal source of pressure is not operating.
A normally engaged brake that is released or disengaged by hydraulic pressure comprises a simple and practical means for providing an emergency or parking brake that is energized in the event of hydraulic failure or shut-down. Thus, by relieving the hydraulic pressure to the brake, a driven or otherwise rotating member can be held in a fixed position. This type of brake has a wide range of application as for example between a hydraulic motor and a gearbox. Additionally, such a brake may be suspended or hung from the end of a hydraulic motor or other source of power, or may be used in vehicle power trains, machine tools, cable wheels, servo mechanism applications and generally as a brake on any rotating shaft. Such a normally engaged brake that is disengageable by hydraulic pressure is disclosed in U.S. Pat. No. 3,863,038 to Kreitner et al, the disclosure of which is incorporated herein by reference, and need not be described in detail.
In a system using such a brake, when a failure occurs in the hydraulic system connected to the brake, the brake is automatically applied and thus, the shaft to which the brake is attached cannot be rotated until hydraulic pressure is once again restored. In many cases, it will be desirable to release the brake by use of an auxiliary source of pressure before the principal source of hydraulic pressure is returned to operation. For example, should the hydraulic failure occur in a vehicle equipped with such a brake, it would be desirable to release the brake so that the vehicle could be towed or pushed from the area where the failure occured to an appropriate area to repair the hydraulic system.
Prior to the present invention, a simple hand pump was suggested to release the brake in such cases, however, this approach creates at least two major problems. Firstly, hand pumps typically have a pressure rating of from 7,000 to 10,000 psi. Therefore, without a pressure gauge in the hand pump line, it is possible to exceed the pressure rating of the bake which is typically on the order of 3,000 psi. Moreover, pressures on the order of 7,000 to 10,000 psi are capable of doing permanent damage to the internal components of the brake. Secondly, the pressure applied to the brake by the hand pump must be manually released after the primary or principal source of hydraulic pressure is restored. If release of the auxiliary pressure is overlooked, the main safety feature of the brake will obviously be lost, since with the auxiliary pressure still present, the brake will not engage at all.